Metal material with thermodynamic anisotropy and a method of preparing the same

ABSTRACT

A metal material having thermodynamic anisotropy has an X-axis hardness of 160-180 HV, an X-axis hardness thermal expansion coefficient of 5×10−6-100×10−6 K−1; a Y-axis hardness of 160-180 HV, a Y-axis hardness thermal expansion coefficient of 5×10−6-100×10−6 K−1; and a Z-axis hardness of 180-250 HV, a Z-axis hardness thermal expansion coefficient of 50×10−6-1000×10−6 K−1. A method for preparing a metal material having thermodynamic anisotropy is also disclosed.

The present invention is a Divisional Applications of U.S. applicationSer. No. 16/982,262, filed on Sep. 18, 2020, and now U.S. Pat. No.11,242,607, which is the National Stage Application ofPCT/CN2019/076687, filed on Mar. 1, 2019, which claims priority toChinese Patent Application No.: 201811090322.4, filed on Sep. 18, 2018,which is incorporated by reference for all purposes as if fully setforth herein.

FIELD OF THE INVENTION

The present invention relates to the field of metal materials, and inparticular, a metal material having thermodynamic anisotropy and amethod for preparing the same.

BACKGROUND OF THE INVENTION

Single crystals have physical properties when measured in differentdirections, i.e., anisotropy, while metallic materials generally do notexhibit anisotropy. Metal materials are often polycrystalline, withdifferent crystal orientations and overall isotropic (pseudo-isotropic).The crystal orientation of the processed metal tends to be uniform,exhibiting anisotropy. For example, rolling (especially hot-rolled)steel sheets tend to exhibit anisotropy in the rolling direction and thevertical rolling direction due to the crystal fibers extending along therolling direction. Therefore, the mechanical properties of the steelsheet vary greatly in the rolling direction and the directionperpendicular to the rolling direction.

Most metals are polycrystalline, so they usually do not have anisotropy.They may have a certain anisotropy after machining, but it is difficultto make fine metal materials with anisotropy that are suitable for micromotors and micro sensors. Micro-Electro-Mechanical Systems, Internet ofThings, Smart Devices all use micro motors and micro sensors. Newanisotropic metal materials are urgently needed for making micro motorsand micro sensors to meet the increasing demand.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a metal materialhaving thermodynamic anisotropy. The metal material has an X-axishardness of 160-180 HV, an X-axis hardness thermal expansion coefficientof 5×10⁻⁶-100×10⁻⁶ K⁻¹; a Y-axis hardness of 160-180 HV, a Y-axishardness thermal expansion coefficient of 5×10⁻⁶-100×10⁻⁶ K⁻¹; and aZ-axis hardness of 180-250 HV, a Z-axis hardness thermal expansioncoefficient of 50×10⁻⁶-1000×10⁻⁶ K⁻¹.

In another embodiment, the metal material is selected from the groupconsisting of copper, tin, silver, nickel, chromium, cobalt, and analloy thereof.

In another embodiment, the X-axis hardness is 140-150 HV, the Y-axishardness is 140-150 HV, and the Z-axis hardness is 190-220 HV.

In another embodiment, the X-axis hardness thermal expansion coefficientis 5×10⁻⁶-10×10⁻⁶ K⁻¹, the Y-axis hardness thermal expansion coefficientis 5×10⁻⁶-10×10⁻⁶ K⁻¹, and the Z-axis hardness thermal expansioncoefficient is 80×10⁻⁶-120×10⁻⁶ K⁻¹.

In one embodiment, the present invention provides a method for preparinga metal material having thermodynamic anisotropy. The method includes(1) providing an electroplating base solution that includes a salt ofthe metal material, an acid; (2) providing additives to theelectroplating base solution, the additive including a brightener, acarrier, a leveling agent, a surfactant, and an antioxidant; (3) mixingthe additives with the electroplating base solution to form anelectroplating solution; and (4) conducting a direct current platingprocess to form the metal material.

In another embodiment, the metal salt is copper sulfate, eithercontaining tin ions, silver ions, nickel ions or cobalt ions, and in theelectroplating base solution, the metal salt has a concentration of 10to 100 g/L; the acid is sulfuric acid, or other corresponding acids, andin the electroplating base solution, the acid has a concentration of10-100 g/L.

In another embodiment, the brightener is an organosulfate having formula(I):

in formula (I), X is O or S; n is 1 to 6; M is hydrogen, alkali metal,or ammonium; R₁ is an alkylene, cyclic alkylene group of 1 to 8 carbonatoms, or an aromatic hydrocarbon of 6 to 12 carbon atoms; and R₂ isMO₃SR₁, and in the electroplating solution, the brightener has aconcentration of 1-10 mL/L.

In another embodiment, the organosulfate is sodium lauryl sulfate,disodium 3,3-dithiobispropane-sulphonate, or 3,3′-dithiobispropanesulfonic acid.

In another embodiment, the carrier is a copolymer of ethylene oxide andpropylene oxide, and in the electroplating solution, the carrier has aconcentration of 10-20 mL/L.

In another embodiment, the leveler is

and in the electroplating solution, the leveler has a concentration of30-70 mL/L.

In another embodiment, the surfactant is polyethylene glycol, and in theelectroplating solution, the surfactant has a concentration of 20-120mL/L.

In another embodiment, the antioxidant is sorbic acid or citric acid,and in the electroplating solution, the antioxidant has a concentrationof 10 g/L.

In another embodiment, the direct current plating process is conductedat a current density of 2-30 A/dm².

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 shows the measurement and calculation of thermal expansioncoefficients in the X-axis, Y-axis and the Z-axis directions.

FIG. 2 shows the thermal expansion coefficients of the metal material ofExample 3 in the X-axis, Y-axis and the Z-axis directions.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, example of which is illustrated in the accompanying drawings.

For convenience of description, the examples all use an anisotropiccopper material as an example. The present invention is not limited tocopper. Metal materials containing tin, silver, nickel, chromium,cobalt, or an alloy thereof can also be prepared by the same method asthe copper material.

Example 1

Preparation of a Metal Material with Thermodynamic Anisotropy (Hardnessin the X-Axis, Y-Axis, and Z-Axis Directions).

A copper sulfate solution having a divalent copper ion concentration of40 g/L, a sulfuric acid solution having a sulfuric acid concentration of120 g/L, and a hydrochloric acid having a chloride ion concentration of50 ppm were mixed and stirred for two hours to form an electroplatingbase solution. Electroplating additives, a brightener (accelerator), themain component being an organosulfate having formula (I); a carrier, themain component being polyethylene glycol; and a leveler, the maincomponent being a quaternary ammonium salt having formula (II), wereadded to the electroplating base solution form an electroplatingsolution. The concentration of the brightener in the electroplatingsolution was 4 mL/L; the concentration of the carrier in theelectroplating solution was 15 mL/L; and the concentration of theleveler in the electroplating solution was 35 mL/L.

A substrate was plated in the electroplating solution for 40 minutes ata current density of 5 A/dm².

After electroplating, the copper film was gently peeled off from thesubstrate. The hardness values of the copper film in the X-axis, Y-axis,and the Z-axis directions were measured in a microhardness test.

The test results were as follows: X-axis microhardness: 143.28 HV;Y-axis hardness: 145.44 HV, and the Z-axis microhardness: 201.47 HV. Thecopper film had significant hardness anisotropy.

Example 2

Preparation of a Metal Material with Thermodynamic Anisotropy (ThermalExpansion Coefficient in the X-Axis, Y-Axis, and Z-Axis Directions).

A copper sulfate solution having a divalent copper ion concentration of50 g/L, a sulfuric acid solution having a sulfuric acid concentration of100 g/L, and a hydrochloric acid having a chloride ion concentration of50 ppm were mixed and stirred for three hours to form an electroplatingbase solution. Electroplating additives, a brightener (accelerator), themain component being an organosulfate having formula (I); a carrier, themain component being polyethylene glycol; and a leveler, the maincomponent being a quaternary ammonium salt having formula (II), wereadded to the electroplating base solution form an electroplatingsolution. The concentration of the brightener in the electroplatingsolution was 4 mL/L; the concentration of the carrier in theelectroplating solution was 10 mL/L; and the concentration of theleveler in the electroplating solution was 70 mL/L.

A substrate was plated in the electroplating solution for 20 minutes ata current density of 10 A/dm².

FIG. 1 shows the measurement and calculation of thermal expansioncoefficients in the X-axis, Y-axis and the Z-axis directions.

After electroplating, the copper film was peeled off from the substrate.The thermal expansion coefficients of the copper film in the X-axis,Y-axis and the Z-axis directions were measured by a mechanical thermalexpansion analyzer (Nexus, Germany), temperature rising range: 20-400°C.

The test results were as follows: at 20-400° C., thermal expansioncoefficient in the X-axis direction: 6.8×10⁻⁶/K; thermal expansioncoefficient in the Y-axis direction 6.9×10⁻⁶/K; and thermal expansioncoefficient in the Z-axis direction 91.7×10⁻⁶/K.

Thermal expansion coefficient in the Z-axis direction is more than 10times higher than those in the X-axis and Y-axis directions.

Example 3

Preparation of a Metal Material with Thermodynamic Anisotropy (ThermalExpansion Coefficient and Etching Resistance in the X-Axis, Y-Axis, andZ-Axis Directions).

A copper sulfate solution having a divalent copper ion concentration of60 g/L, a sulfuric acid solution having a sulfuric acid concentration of80 g/L, and a hydrochloric acid having a chloride ion concentration of60 ppm were mixed and stirred for three hours to form an electroplatingbase solution. Electroplating additives, a brightener (accelerator), themain component being an organosulfate having formula (I); a carrier, themain component being polyethylene glycol (a mixture of polyethyleneglycol with molecular weight of 4000 and polyethylene glycol withmolecular weight of 800); and a leveler, the main component being aquaternary ammonium salt having formula (II), were added to theelectroplating base solution form an electroplating solution. Theconcentration of the brightener in the electroplating solution was 6mL/L; the concentration of the carrier in the electroplating solutionwas 10 mL/L; and the concentration of the leveler in the electroplatingsolution was 30 mL/L.

A substrate was plated in the electroplating solution for 20 minutes ata current density of 15 A/dm².

After electroplating, the copper film was peeled off from the substrate.The thermal expansion coefficients of the copper film in the X-axis,Y-axis and the Z-axis directions were measured by a mechanical thermalexpansion analyzer (Nexus, Germany), temperature rising range: 20-400°C.

The test results were as follows: at 20-400° C., thermal expansioncoefficient in the X-axis direction: 153×10⁻⁶/K; thermal expansioncoefficient in the Y-axis direction 160×10⁻⁶/K; and thermal expansioncoefficient in the Z-axis direction 2928×10⁻⁶/K. FIG. 2 shows thethermal expansion coefficients in the X-axis direction or Y-axisdirection and the thermal expansion coefficients in the Z-axisdirection.

Thermal expansion coefficient in the Z-axis direction is more than 20times higher than those in the X-axis and Y-axis directions.

The etching rate determination includes the following steps: wafercutting (3 cm*4 cm), wafer plating (10ASD*12 min), cleaning (DI water),drying (90° C.*1 hour), weighing G1, soft etching 2 minutes, cleaning(DI water), drying (90° C.*1 hour), weighing G2, morphology (OM). Theplating area was 3 cm*3 cm, and etching solution was H₂SO₄/H₂O₂/additiveFE830. The etching rates are calculated by weighing method. The resultsare shown in the table below.

X-axis Y-axis Z-axis Example 3 0.06 μm/min 0.06 μm/min 0.18 μm/minComparative Example 0.14 μm/min 0.14 μm/min (Market Leader)

The etching rates were measured under the same condition, andcomparative example was prepared using current market leaderelectroplating solution and method.

These materials of the present inventions can be used as a component ofthe temperature-controlled micromotor. Because the Z-axis direction hasa large thermal expansion coefficient and hardness, thetemperature-controlled micromotor prepared by the material will havelarge torque, and thus is stable and safe.

The methods described use an electroplating base solution of a metalsalt and an acid, electroplating additives and a DC electroplatingprocess, and have the following advantages:

First, a regular electroplating process is used and reduces thecomplexity of the mechanical processing scheme; precision can be reachedmicron level; and no specialized equipment is required. Second, theelectroplated metal or alloy material has thermodynamic anisotropy,especially the thermal expansion coefficient and etching resistance.Third, the additives can carry a high current density, thereby achievinghigh-speed plating, so the production efficiency is improved.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method for preparing a metal material havingthermodynamic anisotropy comprising: (1) providing an electroplatingbase solution that includes a copper sulfate solution having a divalentcopper ion concentration of 40 g/L, a sulfuric acid solution having asulfuric acid concentration of 120 g/L, and a hydrochloric acid having achloride ion concentration of 50 ppm; (2) providing additives to theelectroplating base solution, the additives including a carrier, asurfactant, an antioxidant, an organosulfate having a concentration of 4mL/L, and a leveler having a concentration of 35 mL/L; (3) mixing theadditives with the electroplating base solution to form anelectroplating solution; and (4) conducting electroplating at a currentdensity of 5 A/dm² for 40 minutes to form the metal material, whereinthe carrier is a copolymer of ethylene oxide and propylene oxide, thesurfactant is polyethylene glycol, the antioxidant is sorbic acid orcitric acid, the organosulfate is sodium lauryl sulfate, disodium3,3-dithiobispropane-sulphonate, or 3, 3′-dithiobispropanesulfonic acid;and the leveler is


2. The method of claim 1, wherein in the electroplating solution, thecarrier has a concentration of 10-20 mL/L.
 3. The method of claim 1,wherein in the electroplating solution, the surfactant has aconcentration of 20-120 mL/L.
 4. The method of claim 1, wherein in theelectroplating solution, the antioxidant has a concentration of 10 g/L.